[R] Need frequency distribution for x,y coordinates

[Roger Bivand]

On Sat, 11 Feb 2006, mark shanks wrote:

> Hi,
> 
> I have a set of data in x,y coordinates across the range of -5 to 5 in each 
> dimension. I would like to obtain the frequency distribution of the 
> different points, and then graph them so you can see which of the points are 
> the most frequently occurring.
> 
> This would seem to be easy in Matlab, which has the hist3 command for doing 
> frequency distributions/histograms in 3 dimensions. However, as far as I can 
> tell, R does not have a hist3 command.

See contributed package ash, function bin2:

> xy <- cbind(x=runif(250,-5,5), y=runif(250,-5,5))
> bins <- bin2(xy, ab=matrix(c(-5,-5,5,5),2,2))
> image(bins$nc)

or

> filled.contour(bins$nc)

Using the x and y arguments to image or filled.contour, you can set the 
axes, and asp=1 to preserve aspect.

See also function kde2d in package MASS - included in the standard 
distribution.

IMO, 3D histograms can mislead because perception depends on viewer 
position. All of the above give readily interpreted visualisations based 
on colour class intervals.

> 
> Is there any easy way to do this in R? I'm investigating whether matlab or R 
> is more suitable for our needs, but don't want to reject R due to my present 
> ignorance of its functions.
> 
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-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no